People over-think and under-think this stuff quite often. In this case you are over-thinking.
Speakers typically have a power rating. That's the MOST power that a speaker should be fed before it is damaged.
A/V receivers typically have a power rating. That's the most power it can deliver, steadily, without over heating.
At 'normal' listening levels, you will feed a speaker far less power than it can handle, and the receiver will be delivering far less power than it is capable of putting out.
If you like to crank it up loud, then you need to start thinking about things a lot, because you can't really get a lot of quality audio for a cheap price. You just spend a lot more, and you get a lot more. But, for a first time system, it doesn't matter that much. You just want the most your budget allows for. Go listen to speakers you can afford, and pretty much any entry level A/V receiver will drive those speakers at reasonable levels, and the A/V receivers will all sound very similar to each other. Denon, Marantz, Yamaha, Pioneer, Onkyo. They are all similar at the lower price points and have similar sound and build quality. Some give a few more features, some have a bit better build quality, but they all sound similar and are close.
Prepackaged systems don't add to the quality or ease of setup by much, if at all. You tend to get a bit more quality if you are willing to invest time into listening to speakers, and if you are willing to take some recommendations and look for sales. Some refurb or used items may offer a great deal more product and quality for the money if you want to go that route. For connectivity, you just need some speaker wires and a subwoofer (coaxial) wire. We are more than willing to help you buy the right wires. Worth saying that many home theater in a box kits use very low quality wiring, which you shouldn't really use anyway.
As for your sources, I think you should start with your XB1, and go from there. A good A/V receiver will allow you to add things moving forward, so you can wait and decide later if you are happy, or want something more.